1. Field of the Invention
The present invention relates in general to Satellite Positioning System (SATPS) systems, and in particular to generic Satellite Positioning System (SATPS) receivers and related methods.
2. Description of the Related Art
Use of wireless communicators such as cellular telephones, Personal Communication System (PCS) devices, and Personal Data Assistant (PDA) devices, has become commonplace. Such devices can provide voice, data, and other services, such as internet access, affording many conveniences to cellular system users.
The cellular and PCS arenas have recently integrated Satellite Positioning System (SATPS) technology, including Global Positioning System (GPS) technology, into wireless transceiver devices such as the cellular telephone. For example, U.S. Pat. No. 5,874,914, issued to Krasner, which is incorporated by reference herein, describes a conventional method wherein the basestation (also known as the Mobile Telephone Switching Office (MTSO)) transmits GPS satellite information, including Doppler information, to a remote unit using a cellular data link, and then computes pseudoranges to the in-view satellites without receiving or using satellite ephemeris information.
This current interest in integrating GPS with cellular telephony stems from a recent Federal Communications Commission (FCC) regulations requiring that cellular telephones be locatable within 20 feet when an emergency call, such as a “911” call (also referred to as Enhanced 911 or “E911”), is placed by a given cellular telephone. Such position data can assist police, paramedics, and other law enforcement and public service personnel, as well as other agencies seeking to determine the position of a particular wireless communicator such as a cellular telephone.
GPS data that is supplied by the MTSO in the Krasner system can be used by the cellular user for other purposes. For example, the GPS data may be used by to determine information such as directions, particular locations that the cellular user is trying to locate, relative location of the cellular user to other landmarks, directions for the cellular user via internet maps or other GPS mapping techniques, not to mention other purposes. Thus, this data can be very useful to cellular and PCS subscribers because such data can be utilized for purposes other than E911 calls.
In Krasner's methodology, the number of data links that can be connected to a GPS-dedicated data supply warehouse can be limited. Such a server/GPS data supply location, whether at the MTSO or other locations in the cellular network, can require that the cellular telephone maintain two data links. One data link is needed for voice and/or cellular subscriber data used by the cellular subscriber to transmit and receive voice and/or data that the cellular subscriber is using, e.g., talking with another person, sending data across the cellular network, etc. In addition, another data is needed for the GPS information that is being sent by the MTSO/cellular network server to the cellular subscriber.
Conventional cellular telephones are not capable of operating in such a manner. Conventional cellular telephones would therefore either be required to (1) maintain two voice/data links simultaneously, and/or (2) switch between two data links in time. One link would be used to transmit their voice and/or data during cellular use, and another link would be used for the GPS data link. This can result in higher charges for the cellular subscriber, as well as overloading cellular system bandwidth.
In digital cellular systems, it is possible for a single data link to support both voice and GPS data communications simultaneously, but there is a cost in terms of available link data rate for voice. In CDMA systems, for example, the additional burden of the GPS data link will increase the total data transmission requirement, and therefore decrease the available range for voice communications at a fixed bit error rate.
As a result, GPS equipped telephones that are deployed in a cellular system described by Krasner, would use more bandwidth as the present cellular system. This can be problematic especially since the available bandwidth is overloaded. Alternatively, additional cells could be installed in a Krasner-based system, but this would most likely increase the capital outlay for the cellular telephone network.
Further, in Krasner the location of the “basestation” is required to be within 150 km of the cellular subscriber at the time the cellular subscriber is using the wireless handset. When a cellular subscriber is roaming outside of the home service area, or the MTSO is located at a centralized site for a large cellular network, such as AT&T and Verizon Wireless, the Krasner system would require additional MTSO sites throughout such networks. This can make the networks more costly and less efficient. As such, the FCC mandate for E911 calls would be difficult if not impossible to achieve using conventional systems such as the Krasner system.
SATPS receivers used in SATPS systems typically need an unobstructed view, or, at least a mostly unobstructed view, of the sky to receive the SATPS signals. However, wireless communications devices such as cellular telephones, PDA's and PCS devices, are commonly used in situations where the view of the sky is occluded, for example, by large buildings in urban areas (also known as urban canyons). This can make position determination difficult for SATPS receivers. These situations make delivery of consistent, accurate position information difficult. Many solutions have been proposed, such as pseudolite deployment, but such solutions are typically expensive and based on the SATPS infrastructure itself. Consequently, institutions such as local businesses and local governments cannot affect the delivery of more accurate position information.
Using SATPS data for other purposes, such as for location services, is also becoming more commonplace in other types of environments, such as Personal Data Assistants (PDAs). Using SATPS data with other types of wireless networks such as local wireless networks (such as Bluetooth), Short Message Service (SMS), Citizens Band (CB) radio, automotive navigation systems, and other devices is also being contemplated.
However, the requirements of a SATPS receiver for each of these environments are quite different. For example, in a hand-held device, battery power conservation is more important than in an automotive application. Further, some SATPS assistance data may be available in one application that is not available in another. For example, almanac and ephemeris information may be available in a cellular or wireless environment, but may not be available in, for example, an automotive environment.
Conventional SATPS receivers have been designed for a specific application, and depending upon the particular SATPS receiver application many of the outputs and inputs may not be available. In some cases, many of the outputs and inputs are simply disabled, or are otherwise removed from the SATPS receiver due to, for example, design constraints and/or lack of external access to the SATPS receiver. In other cases, many of the outputs and inputs are simply not designed as part of the SATPS receiver.
As such, SATPS receivers useable in one environment may not be useable in another. Conventional SATPS receivers may also present problems when called upon to deliver different types of outputs that are not typically used in conjunction with the particular application for which they are designed. This can make the design and manufacture of SATPS receivers more expensive and more time consuming.
Accordingly, there is a need in the art for improved SATPS receivers that can potentially be implemented in more than one environment and/or application. It would be highly desirable to provide SATPS receivers that can provide different types of outputs so that the SATPS receivers can be utilized by different applications and/or different operating environments. It is also highly desirable to accomplish both of these objectives without substantially increasing the cost and/or complexity of the SATPS receivers.